Control device for cranes



April 9, 1963 R. B. M KINNON CONTROL DEVICE FOR CRANES 2 Sheets-Sheet 1 Filed Aug. 24, 1961 Immfll 1mm April 9, 1963 R. B. MOKINNON CONTROL DEVICE FOR CRANES 2 Sheets-Sheet 2 Filed Aug. 24, 1961 United States Patent Ofifice 3,084,805 Patented Apr. 9, 1963 3,684,805 CONTROL DEVICE FOR CRANES Robert B. McKinnon, BR. 1, P0. Box 26, Harmon, Ontario, Canada Filed Aug. 24, 1961, Ser. No. 133,654 Claims. (Cl. 212-21) This invention relates to a control system for cranes, and in particular it relates to a simplified control for a crane using two control levers to cause three, four or more different crane operations.

In the past it has been customary to provide the operator of a large crane with a panel having three, four or more operating levers. For example, in an overhead crane, a first lever may be moved forwards and backwards to raise and lower a crane hook, a second lever may be moved forwards and backwards to cause travel of a carriage or trolley forwards and backwards along a bridge, and a third lever may be moved forwards and backwards to cause the bridge to travel left and right along side rails. These are the fundamental operations or movements of an overhead crane, but additional operations are frequently required which necessitates further control levers. Thus, there may be an additional lever to switch current on and off to an electromagnet provided to carry loads of magnetic material, there may be an additional lever to cause rotation of the load for aligning the load in a particular direction or directions, and there may be an additional lever to raise or lower an auxiliary crane hook.

Other types of crane such as a gantry crane also have control panels with three, four or more control levers.

It will be apparent that a crane operator cannot have more than two such control levers under constant control, and it is necessary for the operator to move his hands from lever to lever in any sequence of operations normally required of him. It will also be apparent that the control levers do not necessarily have a relation between their movement and that of the crane hook. Consequently it has been necessary for an operator to have a long training period to develop skill and experience necessary for accurate and rapid performance.

Because it is necessary for an operator to move his hands from lever to lever in the aforementioned control system, it is not usual to provide a so called dead man control, that is, the levers normally remain in the position in which they were placed. It is of course, desirable to have a dead man control which returns to a neutral or off position when the operators hand is taken from the control lever.

Another prior art crane control was devised to overcome some of the disadvantages of the aforementioned control. This other type uses only a single control lever to control the three basic crane operations. The single lever may be moved forwards and backwards, left and right, and up and down to cause the crane hook to move in like directions. This control relates control lever movement to crane hook movement, but the control is complex and expensive. The mechanism used is such that the movement of the control lever in a given direction depressed one, two or three push-button type switches depending on the degree of movement of the lever. The push-button switches provide speed control in three discrete steps. While three steps of speed control, or even fewer, may be sufiicient for some auxiliary crane operations, it is desirable to have a greater degree of speed control at least for the three basic or fundamental crane operations. Because of the complex nature of this prior art control it is difiicult to increase the number of steps of speed control in the three operations.

The present invention seek-s to overcome disadvantages of prior crane controls by an improved two lever crane control.

It is an object of this invention to provide a relatively simple and inexpensive crane control which controls crane operations by two control levers.

It is another object of this invention to provide an improved crane control system where the operator is not required to remove his hands from the two control levers during crane operation.

It is yet another object of this invention to provide a crane control wherein a fine control of speed in the main crane operations may be achieved.

Other objects and advantages of the invention will be apparent from consideration of the following description taken in conjunction with the drawings in which:

FIGURE 1 is a side elevation showing very generally a three motor overhead crane embodying the present invention,

FIGURE 2 is a partial top view showing the two control levers used in the control system according to the invention,

FIGURE 3 is a schematic wiring diagram of the motor control circuits of a crane adapted to the present control system,

FIGURE 4 is a partial view of a contact member shown in FIGURE 3 on an enlarged scale,

FIGURE 5 is a side elevation, partly in section, of one of the control levers used in the present invention and showing some adjacent apparatus,

FIGURE 6 is a partial view of the control lever of FIGURE 5 taken along line 66 of FIGURE 5, and

FIGURE 7 is a side elevation, partly in section, of a modification of one of the control levers used in the present invention.

Briefly, the present invention is a control system for controlling at least three basic crane operations or movements with two control levers. Three sets of switch contacts control the directions of rotation of the three motors, and three rheostats control the speed of rotation. A first control lever is pivotally mounted to move in opposite directions from a neutral position to engage first switch contacts and vary the resistance of a first rheostat. A second control lever is movable in any planar direction from a neutral position, and has means to engage second switch contacts and vary the resistance of a second rheostat upon movement in a first direction from a first line extending through the neutral position and in a direction opposite thereto. The second lever also has means to engage third switch contacts and vary the resistance of a third rheostat upon movement in a second direction from a second line extending through the neutral position at right angles to said first line and in a direction opposite said second direction. Additional control devices may be added to the first lever to perform auxiliary operations.

Referring now to FIGURE 1, a well known type of overhead crane is shown generally, having a bridge 10 equipped with wheels 11 which are supported by rails 12 for movement of the bridge transversely to the length of the bridge. The rails 12 are fixed to walls 14 or other convenient supporting structure. A wheeled carriage or trolley 15 is provided with wheels 16 which are supported by the bridge 10 for movement along the length of the bridge. A hoisting mechanism is carried by trolley 15 for raising and lowering a crane hook 18.

Three electric driving motors (not shown in FIGURE 1) drive the crane. A first driving motor drives the hoisting mechanism to raise and lower the crane hook 18; a second motor drives the trolley 15 back and forth along the bridge 10; and a third motor drives the bridge transversely to and fro. This is well known in the art. The controls for controlling the motors and operating the crane are generally located in an operators cab 20 suspended beneath bridge lt) towards one end. According to the present invention two control levers 21 and 22 mounted in casing 17 are used to control the three driving motor-s. In FIGURE 1 the lever 21 is shown in its neutral or off position whereas lever 22 is shown moved toone side of its neutral position so that levers 21 and 22 can be seen separately.

The levers 21 and 22 as mounted in casing 17 are shown in a top view in FIGURE 2. Here the levers 21 and 22 are both shown in their neutral positions. The lever 21 is pivotally mounted at its lower end for movement in opposite directions from its neutral position. The lever 22 is mounted so that it is movable in any planar direction from its neutral position, that is, the control knob at the upper end of lever 22 may move in any planar direction as indicated by the arrows. Lever 22 is restrained from vertical movement by its mounting. The mounting means for lever 22 is shown in more detail in FIGURES 5 and 6 and will be described in connection with these figures hereinafter. It is desirable to relate crane hook movement to control movement where possible. A preferred control uses lever 21 to control the hoisting motor while lever 22 controls the movement of the trolley and bridge. Thus, the righthand control lever 22 may have its movement related to the direction of movement of the trolley and bridge.

Referring now to FIGURE 3 which shows the schematic wiring diagram of the control circuit, the three driving motors are indicated at 24, 25 and 26. These motors are indicated as three phase, wound rotor, induction motors with the rotor winding brought out to slip rings. It will, however, be apparent that single phase induction motors or direct current motors could be used as driving motors for the crane. The motors 24, 25 and 26 drive the hoisting mechanism, trolley and bridge respectively, however the circuitry associated with each motor is similar. Consequently, it is believed that a description of the circuitry of motor 24 is sufiicient for an understanding of FIG- URE 3.

Motor 24 comprises a stator 27 and a rotor 28. The stator may be connected in a delta connection as shown or a Y connection to a three phase power source 31, 32, 33 through either the contacts of switches 34, 35, 36 or 37, 38, 39 Whichever are closed. The normally open switches 34, 35, 36 are operated to a closed condition when a solenoid '40 is energized, and switches 37', 38, 39 are operated to a closed condition when a solenoid 41 is energized. These two sets of switches constitute a reversing switch for motor 24 as is well known.

The windings of rotor 28 are brought out to three slip rings indicated at 43, 44, 45 which are connected through rheostats 46, 47, 48 to a common point such as ground. The rheostats 46, 47, 4 8 are connected to insert resistance in the rotor circuit of motor 24 to reduce the speed of rotation of the rotor. The rheostats 46, 47, 48 have movable contact members or arms 50, 51, 52 respectively which are mechanically connected one to the other and to control lever 21 by a linkage 42. The rheostats 46, 47, 48 may constitute parts of a multiple section rheostat positioned adjacent lever 21 with a short linkage extending between lever 21 and the multiple rheostat. As the lever 21 is moved away from its neutral position in either direction, the arms 50, 51, 52 move accordingly away from their neutral position. ,As the arms 50, 51, 52 move over the resistance of the rheostats 46, 47, 48 in a direction away from their center position, theresistance added to the rotor circuit by the rheostats is decreased. Thus, as lever 21 is moved away from its neutral position, the speed of rotation of motor 24 is increased. This is so regardless of the direction in which lever 21 is moved away from neutral. This type of speed control of motors is known in the art and further detail is believed unnecessary. Because of the use of rheostatsin the speed control it is possible to achieve a fine control of speed.

In order to have control of the direction of rotation of motor 24, the solenoid 41} should be energized when lever 21 is moved in one direction from its neutral position and solenoid 41 when the lever is moved in the opposite direction. This will close either switches 34, 35, 36 or switches 37, 38, 39. The solenoids can be energized in the aforementioned manner by many switch means known in the art. FIGURE 4 shows one means comprising contact strips 53 and 54 extending to one side of arm 50 when arm 50 is in its center position as shown. A bridging member 55 is carried by arm 50 and insulated therefrom by an insulating arm 56. The member 55 does not bridge the contact strips 53 and 54 when arm 50 is in its center or neutral position, but does so as soon as arm 50 moves from its center position in the direction of the contact strips. When bridging member 55 connects strips 53 and 54, a circuit is completed through solenoid 48. The circuit is from power source conductor 33, through solenoid 48, through conductor 57 to contact strip 53, across bridging member 55 to contact strip 54 and thence by conductor 58 to the power source conductor 32.

Similarly, contact strips 69 and 61 on the other sideof arm 50, in conjunction with a bridging member 62, can complete a circuit through solenoid 41 when arm 50 is moved from its center position towards the strips 60 and 61. The lever 21 therefore has control over both direction and speed of rotation of motor 24.

The wiring for motors 25 and 2 6 is similar to that for motor 24. However, the control lever 22 is mechanically connected by linkages 65 and 66 to the rheostats and solenoid switches for controlling speed and direction of rotation of both motors 25 and 26. The linkages are better understood by reference to FIGURES 5 and 6.

In FIGURES 5 and 6 the control lever 22 is shown mounted at its lower end in a ball and socket type joint 70. Any type of joint which permits movement of the upper or handle end of lever 22 in all planar directions is suitable. Four springs '71, 72, 73 and 74 are connected between the four sides of lever 22 and casing 17. At the outer end the springs 71, 72, 73, 74 are fastened to an adjusting screw 75, 76, 77, 78 respectively so that the tension exerted by each spring may be adjusted. The screws 75, 76, 77, 78 threade-dly engage casing 17 and are restrained from unwanted rotation by lock nuts. The springs 71, 72, 73, 74- exert sufficient force on lever 22 to cause it to return to its neutral position when the handle of lever 22 is released. This creates the so-called dead man control.

It will be apparent that only two springs would be required for pivotally mounted handle 21 in order to have it return to neutral when released. Thus, the spring return for lever 21 is similar to that of lever 22 for example in the plane shown in FIGURE 5. It is believed to be unnecessary .to describe this in detail for lever 21. t

The control lever '22 is provided with universal joints 80 and 81 on two sides at right angles to one another. Connecting members 82 and 83 extend from the univer sal joints 80 and 81 respectively. The connecting member 82 is provided with a universal joint connection 85 at its remote end for connection with a movable arm 86 of a rheostat 87. The universal joints 80 and 85 and the connecting member 82 comprise the linkage 65 of FIGURE 3. While only a single rheostat 87 is shown in FIGURE 5 for simplicity, it will be apparent that this may be a triple or multiple rheostat comprising, for example in combination parts 87, 87a and 87b of the schematic diagram of FIGURE 3.

In a like manner the connecting member 83 extends to a universal joint connection with the rheostats '84 for controlling motor 28. The member 83 is thus a part of the linkage 65 of FIGURE 3.

It will be apparent that the manner of linking control lever 22 to control both motors 25 and 26 as shown in FIGURES 5 and 6, will result in some degree of interaction between the controls. To illustrate this by way of example, if lever 22 were moved towards the bottom of the diagram as shown in FIGURE 6, the linkage 66 comprising member 83 will move the rheostat control 84 for motor 26. Ideally, such a movement should not affect motor 25. However, as lever 22 is moved it carries the universal joint 80 with it so that connecting member 82 is at an acute angle to member 83. The arm 86 of rheostat 87 will be pulled by member 82 a short distance towards the control lever 22 which may cause motor 25 to rotate. This interaction may be negligible depending partly on the length of the linkages or the interaction may be permitted because the operator will become accustomed to it and counteract it automatically. There are, however, linkages known that will not cause any interaction between movements in two directions at right angles. While these linkages are of a more complex design they may be readily used in the present invention. An example of such a linkage can be found in United States Reissue Patent 22,785 to Clay dated September 3, 1946 and particularly in FIGURE 6 of this patent.

It will be seen from the description thus far that the invention provides a simple inexpensive crane control using two control levers for controlling three crane motors. The system may be readily adapted to the crane controls presently in use. The rheostat permits a fine control of motor speed for the three basic crane movements or operations.

As was previously mentioned, it is frequently necessary to have auxiliary controls for a crane to enable an operator to control auxiliary operations. One such auxiliary operation is the rotating of the load carried by the crane to align the load in a given direction. Such a control is frequently required, for example, in a crane in a steel mill used to place ingots in a soaking pit. This rotating operation requires an additional electric motor and an additional control. The control can be added quite conveniently by a modification to the control lever 21 as best described with reference to FIGURE 7.

Referring to FIGURE 7, there is shown a partial side elevation of the left hand orpi-votally mounted control lever which is designated 21a. A socket 90 is formed in the upper part of lever 21a to receive a T-shaped handle 91 having an upright 92 and a cross-portion 93. Opposed slots 94 are provided in socket 90 extending laterally around socket 90 for a limited distance. The upright 92 is provided with a hole 95, extending diametrically through the upright, to receive a pin 96. The pin 96 extends from hole 95 through slots 94 to retain the upright 92 in socket 90 while permitting rotational movement of upright 92 within limits where the pin 96 strikes the ends of slots 94.

Two similar switches 98 and 99 are mounted to socket 90, one on each side of a projection 100 which projects from upright 92. Switch 98, which is shown in section, comprises a casing 101 of insulating material with an opening 102 at one end through which projects a rodlike or cylindrical operating member 103. The operating member 103 is mounted for longitudinal inward and outward movement and has a bearing head 97 which bears against projection 100. A spring 105 is compressed between a protrusion or ring 104 on operating member 103 and an inwardly projecting member 106 on casing 101. The spring 105 biases the operating member out wardly against projection 100. The longitudinal movement of member 103 is limited or restricted in an outward direction by ring .104 engaging the end of case 101 and in an inward direction by the contacts becoming engaged as will now be described. The inward end of operating member 103, that is, the end remote from bearing head 97, carries a bridging member 110 with two spaced contacts 111 and 112. While bridging member 110 may be a rigid piece of conducting material with a contact 111 on one end and a contact 112 on the other, it is preferably a piece of resilient conductor having a slight curvature to provide a slight resilient mounting for contacts 111 and 112. The contacts 111 and 112 are designed to engage contacts 114 and 115 when operating member 103 is depressed or moved in an inwardly direction. This would complete a circuit, for example, through contact 114, contact 111, bridging member 110, contact 112 and contact 115 and the switch is then closed. The switch 99 is similarly constructed.

The operation of the control of FIGURE 7 is straightforward. The springs in switches 98 and 99 tend to bias the pin 100 to a central position. The springs have sulficient force to return the pin to this position and thereby return the handle 91 to its neutral position whenever the handle is released. A dead man type of control is thus provided. As the cross portion 93 of handle 91 is turned the upright 92 rotates causing pin 100 to depress the operating member of either switch 98 or 99. This will close the contacts of the particular switch and cause power to be applied to a motor for rotating the crane load in a given direction. For example, the closing of the contacts may energize a solenoid which closes switches between a power source and the motor. Turning handle 91 in the opposite direction will close the contacts of the other switch and cause rotation in the other direction. It is, of course, desirable to have the rotation of the handle in one direction cause rotation of the load in the same direction.

Another auxiliary operation frequently required on a crane is the switching on and off of a current to energize and denergize an electromagnet for carrying loads of magnetic material. The operators control switch for controlling this electromagnet current may be a simple on-off switch which energizes a solenoid operated switch to control the current. Such an operators control switch can be easily added to lever 21. It is convenient to use a snap-action type of pushabutton switch which switches to closed condition on one push and switches to an open condition on the next push. Such switches are well known and can be mounted on lever 21 for operation by the operators thumb.

If it should be required an operators push button control switch for an electromagnet could be mounted on a handle 91 of FIGURE 7 for example at one end of the cross piece 93 for actuation by the operators thumb.

It will be apparent that other types of operations may be controlled by a crane operator by placing the added control on level 21. The control system enables a crane operator to control the three basic crane movements or operations with certain additional operations from two control levers.

I claim:

1. A control system for controlling at least first, second and third driving motors in a crane, comprising first, second and third switch contacts for controlling the direction of rotation of said first, second and third motors respectively, a first, second and third variable resistance means for controlling the speed of rotation of said first, second and third motors respectively, a first control lever movable in opposite directions from a neutral position having means to engage said first switch contacts and vary said first resistance means, and a second control lever movable in any planar direction from a neutral position, said second lever having means to engage said second contacts and vary said second resistance means upon movement in a first direction from a first line extending through said neutral position and in a direction opposite thereto, said second lever having means to engage said third contacts and vary said third resistance means upon movement in a second direction from a second line extending through the neutral position at right angles to said first line and in a direction opposite said second direction.

2. A control system for controlling at least first, second and third driving motors in a crane, comprising first, secspsaeos ond and third switch contacts for controlling the direction of rotation of said first, second and third motors respectively, first, second and third variable resistance means for controlling the speed of rotation of said first, second and third motors respectively, a first control lever movable in o posite directions from a neutral position having means to engage said first switch contacts and vary said first resistance means, first spring means to bias said first lever to its neutral position, a second control lever movable in any planar direction from a neutral position, said second lever having means to engage said second contacts and vary said second resistance means upon movement in a first direction from a first line extending through said neutral position and in a direction opposite thereto, said second lever having means to engage said third contacts and vary said third resistance means upon movement in a second direction from a second line at right angles to said first line and in a direction opposite thereto, and second spring means to bias said second lever to its neutral position.

3. A control system for controlling :at least first, second and third driving motors in a crane, comprising first and second control levers, a pivotal mounting for said first control lever to mount said lever for movement in a first direction and in an opposite direction from a neutral position, first spring means biasing said first lever to its neutral position, a first rheostat means for varying resistance associated with said first motor to vary the speed of rotation thereof, said first lever having means to engage said first rheostat means and vary the resistance thereof in accordance with movement of said first lever, first electrical reversing switches controlling electrical power to said first motor for reversing the direction of rotation thereof, said first reversing switches having first and second positions each corresponding to a direction of rotation, said first reversing switches being actuated to said first position by movement of said first control lever from its neutral position in said first direction and to said second position by movement of said first control lever from its neutral position in a direction opposite said first direction, a universal mounting for said second control lever to mount said second lever for movement in any planar direction from a neutral position, second spring means to bias said second lever to its neutral position, second and third rheostat means for varying resistance associated with said second and third motors respectively to vary the speed of rotation thereof, said second control lever having means to engage said second rheostat means and vary the resistance thereof in accordance with movement of said second lever from its neutral position in a first direction and in a direction opposite said first direction, said second control lever having means to engage said third rheostat means and vary the resistance thereof in accordance with movement of said second lever from its neutral position in a second direction at right angles to said first direction and in a direction opposite said second direction, and second and third electrical reversing switches controlling power to said second and third motors respectively for reversing the direction of rotation thereof, said second and third reversing switches each having a first and a second position corresponding to a direction of rotation, said second reversing switches being actuated to said first position by movement of said second control lever from its neutral position in said first direction and to said second position by movement of said second lever from its neutral position in a direction opposite said first direction, said third reversing switches being actuated to said first position by movement of said second control lever from its neutral position in said second direction and to said second position by movement of said second control lever from its neutral position in a direction opposite said second direction.

4. A control system for controlling at least first, second and third driving motors in a crane, comprising first and second control levers, a pivotal mounting for said first control lever to mount said lever for movement in a first direction and in an opposite direction from a neutral position, first spring means biasing said first lever to its neutral position, a first rheostat means for adding a variable amount of resistance to said first motor connections to cause operation of said first motor at selectable decreased speeds of rotation, a first linkage between said first control lever and said first rheostat means to decrease the resistance added to said first motor by said first rheostat means with movement of said first lever away from its neutral position, first electrical reversing switches controlling electrical power to said first motor for reversing the direction of rotation thereof, said first reversing switches having first and second positions each corresponding to a direction of rotation, said first reversing switches being actuated to said first position by movement of said first control lever from its neutral position in said first direction and to said second position by movement of said first control lever from its neutral position in a direction opposite said first direction, a universal mounting for said second control lever to mount said second lever for movement in any planar direction from a neutnal position, second spring means to bias said second lever to its neutral position, second and third rheostat means for adding a variable amount of resistance to said second and third motor connections respectively to cause operation of said second and third motors at selectable decreased speeds of rotation, a second linkage between said second control lever and said second rheostat means to decrease the resistant added to said second motor by said second rheostat means with movement of said second lever in a first direction from a first line extending through said neutral position and in a direction opposite said first direction, second electrical reversing switches controlling power to said second motor for reversing the direction of rotation thereof, said second reversing switches having first and second positions each corresponding to a direction of rotation, said second reversing switch being actuated to said first position by movement of said second control lever from said first line extending through said neutral position in said first direction and to said second position by movement of said second control lever from said first line in a direction opposite said first direction, a third linkage between said second control lever and said third rheostat means to decrease the resistance added to said third motor by said third rheostat means with movement of said second lever in a second direction from a second line extending through said neutral position at right angles to said first line and in a direction opposite said second direction, and third electrical reversing switches controlling power to said third motor for reversing the direction of rotation thereof, said third reversing switches having first and second positions each corresponding to a direction of rotation, said third reversing switch being actuated to said first position by movement of said second lever from said second line extending through said neutral position in said second direction and to said second position by movement of said second control lever from said second line in a direction opposite said second direction.

5. In a crane having an overhead bridge adapted to travel transversely to its length, a carriage mounted on said bridge for travel lengthwise thereof, a hoisting mechanism mounted on said carriage, a first electric motor mounted on said carriage for driving said hoisting mechanism to raise and lower a load, a second electric motor for moving said carriage back and forth along said bridge, and a third electric motor for moving said bridge to the left and right transversely of its length, a control system comprising first and second control levers, a pivotal mounting for said first control lever to mount said first lever for forward and backward movement from a neutral position in a direction parallel to the length of said bridge, first spring means biasing said first lever to its neutral position, a first rheostat means for adding vairable amounts of resistance to the circuit of said first motor to vary the speed of rotation thereof, said first lever being linked to said first rheostat means to decrease the resistance added by said first rheostat means as said first lever is moved away from its neutral position, first electrical reversing switches controlling electrical power to said first motor for controlling the direction of rotation thereof, said first reversing switches having first and second positions each corresponding to a direction of rotation, said first revers ing switches being actuated to said first position by movement of said first control lever from its neutral position in said forward direction and to said second position by movement of said first control lever from its neutral position in said backward direction, a universal mounting for said second control lever to mount said second lever for movement in any planar direction from a neutral position, second spring means biasing said second lever towards its neutral position, a second rheostat means for adding variable amounts of resistance to the circuit of said second motor to vary the speed of rotation thereof, a first linkage extending from said second control lever to said second rheostat means and arranged to decrease the resistance added by said second rheostat means to the circuit of said second motor as said second lever is moved away from a first line extending through said neutral position substantially at right angles to the length of said bridge, second electrical reversing switches controlling electrical power to said second motor for controlling the direction of rotation thereof, said second reversing switches having a first position corresponding to a direction of motor rotation during said carriage forward along said bridge and a second position corresponding to a direction of motor rotation driving said carriage backward along said bridge, said second electrical reversing switches being actuated to said first position by movement of said second control lever forward from said first line and to said second position by movement of said second control lever backward from said first line, a third rheostat mean-s for adding variable amounts of resistance to the circuit of said third motor to vary the speed of rotation thereof, a second linkage extending from said second control lever to said third rheostat means and arranged to decrease the resistance added by said third rheostat means to the circuit of said third motor as said second lever is moved away from a second line extending through said neutral position substantially parallel to the length of said bridge and third electrical reversing switches controlling electrical power to said third motor for controlling the direction of rotation thereof, said third reversing switches having a first position corresponding to a direction of motor rotation driving said bridge to the left and a second position corresponding to a direction of motor rotation driving said bridge to the right, said third electrical reversing switches being actuated to said first position by movement of said second control lever to the left away from said second line and to said second position by movement of said second control lever to the right away from said second line.

6. A control system for a crane according to claim further including :a snap action push-button switch mounted on said first control lever, said push-button switch being adapted to energize an electromagnet carried by said crane to attract and hold a load of magnetic material.

7. In a crane having an overhead bridge adapted to travel transversely to its length, a carriage mounted on said bridge for travel lengthwise thereof, a hoisting mech anism mounted on said carriage, a first electric motor mounted on said carriage for driving said hoisting mechanism to raise and lower a load, a second electric motor for moving said carriage back and forth along said bridge, a third electric motor for moving aid bridge to the left and right transversely of its length, and a fourth electric motor to rotate the load carried by said crane, -a control system comprising first and second control levers, a pivotal mounting for said first control lever to mount said first 10 v lever for forward and backward movement from :a neutral position in a direction parallel to the length of said bridge, first spring means biasing said first lever to its neutral position, a first rheostat means for adding variable amounts of resistance to the circuit of said first motor to vary the speed of rotation thereof, said first lever being linked to said first rheostat means to decrease the resistance added by said first rheostat means as said first lever is moved away from its neutral position, first electrical reversing switches controlling electrical power to said first motor for controlling the direction of rotation thereof, said first reversing switches having first and second positions each corresponding to a direction of rotation, said first reversing switches being actuated to said first position by movement of said first control lever from its neutral position in said forward direction and to said second position 'by movement of said first control lever from its neutral position in said backward direction, a control handle mounted to said first control lever for limited rotational movement about the axis of said first control lever, first and second electrical switch means mounted to said second control lever, first and second operating members extending from said first and second switch means respectively, means projecting from said control handle engaging said first and second operating members whereby rotation of said control handle in one direction will actuate said first electrical switch and rotation of said control handle in the opposite direction will actuate said second electrical switch, circuit means connecting said first electrical switch means and said fourth motor to cause rotation of said fourth motor in one direction with actuation of said first electrical switch means and connecting said second electrical switch mean and said fourth motor to cause rotation of said fourth motor in the opposite direction with actuation of said second electrical switch means,

a universal mounting for said second control lever to mount said second lever for movement in any planar direction from a neutral position, second spring means biasing said second lever towards its neutral position, a second rheostat means for adding variable amounts of resistance to the circuit of said second motor to vary the speed of rotation thereof, a first linkage extending from said second control lever to said second rheostat means and ar ranged to decrease the resistance added by said second rheostat means to the circuit of said second motor as said second lever is moved away from a first line extending through said neutral position substantially at right angles to the length of said bridge, second electrical reversing switches controlling electrical power to said second motor for controlling the direction of rotation thereof, said second reversing switches having a first position corresponding to a direction of motor rotation driving said carriage forward along said bridge and a second position corresponding to a direction of motor rotation driving said carriage backward along said bridge, said second electrical reversing switches being actuated to said first position by movement of said second control lever forward from said first line and to said second position by movement of said second control lever backward from said first line, a third rheostat means for adding variable amounts of resistance to the circuit of said third motor to vary the speed of rotation thereof, a second linkage extending from said second control lever to said third rheostat means and arranged to decrease the resistance added by said third rheostat means to the circuit of said third motor as said second lever is moved away from a second line extending through said neutral position substantially parallel to the length of said bridge, and third electrical reversing switches controlling electrical power to said third motor for controlling the direction of rotation thereof, said third reversing switches having a first position corresponding to a direction of motor rotation driving said bridge to the left and a second position corresponding to a direction of motor rotation driving said bridge to the right, said third electrical reversing switches being actuated to said first position 1 1 by movement of said second control lever to the left away from said second line and to said second position by movement of said second control lever to the right away from said second line.

8. A control handle for a crane comprising a lever portion and a handle portion mounted for limited rotation to said lever portion, first and second switches having an outer casing mounted to said lever portion, each of said switches having operating members extending from said casings, springs biasing said operating members outwards, first contact means movable by said operating members, and second contact means mounted on said casings, said first and second contact means being actuated to a closed condition by depression of said operating members, means on said handle portion engaging said operating members of said first and second switches whereby rotation of said handle portion in one direction will close the contacts of said first switch and rotation in the other direction will close the contacts of said second switch.

9. A control handle for a crane comprising a lever portion and a handle portion mounted for limited rotation to said lever portion, first and second switches mounted to said lever portion, each of said switches having an outer casing provided with an opening, an operating member extending through said opening for longitudinal movement therethrough, restraining means for limiting the longitudinal movement of said operating members within predetermined limits, springs biasing said operating members longitudinally outwards, first contacts movable by said operating members, and second contacts mounted to said casings, said first and second contacts being actuated to a closed condition by depression of said operating members, means projecting from said handle portion engaging the ends of said operating members of said first and second switches whereby rotation of said handle portion in 12 one direction will close the contacts of said first switch and rotation in the other direction will close the contacts of said second switch.

10. A control handle for a crane comprising a lever portion pivotally mounted at its lower end, a T-shaped handle portion having an upright and a cross portion, said upright being mounted in axially aligned relationship to said lever portion for limited rotational movement, first and second switches each having an outer casing provided with an opening, a cylindrical operating member eX- tending through said opening for longitudinal movement therethrough, restraining means for limiting the longitudinal movement of said operating members within predetermined limits, coil springs biasing said operating members longitudinally outwards, first contacts carried on a resilient mounting on the inner end of said operating member, and second contacts mounted to said casings, said first and second contacts being actuated to a closed condition by depression of said operating members in- Wards, projection means extending from said upright, said first and second switches being mounted to said lever on opposite sides of said projection means with said operating members engaging said projecting means whereby rotation of said handle in one direction will close the contacts of said first switch and rotation in the other direction will close the contacts of said second switch.

References Cited in the file of this patent UNITED STATES PATENTS Re. 22,785 Clay Sept. 3, 1946 2,849,548 Young Aug. 26, 1958 2,857,485 Brooks Oct. 21, 1958 2,913,129 Lindstrom Nov. 17, 1959 

5. IN A CRANE HAVING AN OVERHEAD BRIDGE ADAPTED TO TRAVEL TRANSVERSELY TO ITS LENGTH, A CARRIAGE MOUNTED ON SAID BRIDGE FOR TRAVEL LENGTHWISE THEREOF, A HOISTING MECHANISM MOUNTED ON SAID CARRIAGE, A FIRST ELECTRIC MOTOR MOUNTED ON SAID CARRIAGE FOR DRIVING SAID HOISTING MECHANISM TO RAISE AND LOWER A LOAD, A SECOND ELECTRIC MOTOR FOR MOVING SAID CARRIAGE BACK AND FORTH ALONG SAID BRIDGE, AND A THIRD ELECTRIC MOTOR FOR MOVING SAID BRIDGE TO THE LEFT AND RIGHT TRANVERSELY OF ITS LENGTH, A CONTROL SYSTEM COMPRISING FIRST AND SECOND CONTROL LEVERS, A PIVOTAL MOUNTING FOR SAID FIRST CONTROL LEVER TO MOUNT SAID FIRST LEVER FOR FORWARD AND BACKWARD MOVEMENT FROM A NEUTRAL POSITION IN A DIRECTION PARALLEL TO THE LENGTH OF SAID BRIDGE, FIRST SPRING MEANS BIASING SAID FIRST LEVER TO ITS NEUTRAL POSITION, A FIRST RHEOSTAT MEANS FOR ADDING VARIABLE AMOUNTS OF RESISTANCE TO THE CIRCUIT OF SAID FIRST MOTOR TO VARY THE SPEED OF ROTATION THEREOF, SAID FIRST LEVER BEING LINKED TO SAID FIRST RHEOSTAT MEANS TO DECREASE THE RESISTANCE ADDED BY SAID FIRST RHEOSTAT MEANS AS SAID FIRST LEVER IS MOVED AWAY FROM ITS NEUTRAL POSITION, FIRST ELECTRICAL REVERSING SWITCHES CONTROLLING ELECTRICAL POWER TO SAID FIRST MOTOR FOR CONTROLLING THE DIRECTION OF ROTATION THEREOF, SAID FIRST REVERSING SWITCHES HAVING FIRST AND SECOND POSITIONS EACH CORRESPONDING TO A DIRECTION OF ROTATION, SAID FIRST REVERSING SWITCHES BEING ACTUATED TO SAID FIRST POSITION BY MOVEMENT OF SAID FIRST CONTROL LEVER FROM ITS NEUTRAL POSITION IN SAID FORWARD DIRECTION AND TO SAID SECOND POSITION BY MOVEMENT OF SAID FIRST CONTROL LEVER FROM ITS NEUTRAL POSITION IN SAID BACKWARD DIRECTION, A UNIVERSAL MOUNTING FOR SAID SECOND CONTROL LEVER TO MOUNT SAID SECOND LEVER FOR MOVEMENT IN ANY PLANAR DIRECTION FROM A NEUTRAL POSITION, SECOND SPRING MEANS BIASING SAID SECOND LEVER TOWARDS ITS NEUTRAL POSITION, A SECOND RHEOSTAT MEANS FOR ADDING VARIABLE AMOUNTS OF RESISTANCE TO THE CIRCUIT OF 